WASHINGTON (BLOOMBERG) - Do not wait to get a Covid-19 vaccine booster shot.

That is the overwhelming advice from 15 vaccine experts, infectious disease doctors and public health officials polled by Bloomberg after the rise of the new Omicron coronavirus variant sent vaccine makers rushing to revamp their shots in case new versions are needed.

The highly mutated strain raises new questions about how well existing Covid-19 vaccines will hold up.

But the experts cited a range of reasons for getting an additional dose now, including a lack of sufficient data about Omicron, growing evidence about the benefits of boosters and the months that reformulated shots will likely take to become available.

"Boosters are even more urgent not only to elevate immunity as much as possible for individual protection, but also population-level immunity in terms of the spread of Omicron and the further emergence of new variants," said Dr Gregory Poland, director of the Mayo Clinic's Vaccine Research Group.

Vaccine makers are evaluating the efficacy of their shots against Omicron and developing new, tailored inoculations.

In the United States, where the first cases were identified just this week, the Centres for Disease Control and Prevention (CDC) said all adults should get boosters either six months after receiving Pfizer-BioNTech's or Moderna's two-dose regimen or two months after a Johnson & Johnson jab.

Most experts surveyed aligned with the CDC's recommendation, saying that all adults should receive a booster.

And while the extra doses might not protect fully against Omicron, they "are our best chance, along with other public health measures, of keeping people out of the hospital", said Dr Lois Privor-Dumm, director of adult vaccines at the International Vaccine Access Centre, an advocacy group.

"We don't know enough about Omicron yet to know how well vaccines work, but some protection is better than no protection."

Dr Monica Gandhi, a professor of medicine and an infectious diseases doctor at the University of California at San Francisco, disagreed.

While people 65 and older and those with medical conditions would benefit, "we don't have enough data yet on Omicron to recommend boosters for everyone nor do we know if young healthy people would benefit (or if there would be some adverse effects)", she said.

Dr Paul Offit, director of the vaccine education centre at the Children's Hospital of Philadelphia, who did not participate in the survey, also has reservations about the wide use of boosters beyond high-risk populations.

He noted that myocarditis, a type of heart inflammation that is usually mild and quickly resolves, is a rare risk for young people who get the vaccine.

"There has to be clear benefit in order for you to say the benefits outweigh the risks," said Dr Offit, a member of the Food and Drug Administration's vaccines advisory committee.

The experts surveyed unanimously said people should not wait for new versions of existing vaccines. Boosters will protect recipients from the highly transmissible Delta variant that is now dominant, and could help with the Omicron variant, they said.

"Vaccines and boosters will elevate our antibodies and T cell responses to fight viral infections," said Dr Akiko Iwasaki, a professor of immunobiology at the Yale School of Medicine.

"Even if the antibodies only bind weakly to the Omicron variant (due to the large number of mutations), having enough such antibodies will still reduce the infection, replication and spread," she said, with an additional role played by T cells.

Even if a new drug is needed and becomes available, "boosting now shouldn't preclude boosting with a new version later", said Dr Emily Landon, chief hospital epidemiologist at the University of Chicago Medicine.

And for people who still remain unvaccinated, it is even more important to get immunised, respondents said.

"This is the most important measure and more important than booster doses," said Dr Wilbur Chen, professor at the University of Maryland School of Medicine and a member of the CDC's Advisory Committee on Immunisation Practices.

Most of the experts surveyed said it is too early to judge whether people will need an Omicron-specific shot. Some of them do not anticipate that a separate formula will be needed.

But if new formulations are needed, there will likely be studies examining whether they can be mixed and matched with the previous vaccines, the experts said. That work could come from academia, federal health agencies or the companies themselves, they said.

In the meantime, there are steps that even those who are vaccinated and boosted can take to protect themselves from Omicron.

The most common recommendation, a familiar one by now, was to wear a mask - especially a high-quality, well-fitting one.